1. Field of the Invention
The present invention relates to a positive resist composition and a method of forming a resist pattern that uses the positive resist composition.
Priority is claimed on Japanese Patent Application No. 2010-138536, filed Jun. 17, 2010, the content of which is incorporated herein by reference.
2. Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or electron beam through a mask having a predetermined pattern, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have led to rapid progress in the field of pattern miniaturization.
Typically, these miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation of emission lines of mercury has been used, but nowadays KrF excimer lasers and ArF excimer lasers are now starting to be introduced in mass production. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and higher energy) than these excimer lasers, such as electron beam, extreme ultraviolet radiation (EUV), and X ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material which satisfies these conditions, a chemically amplified resist composition is used, which includes a base component that exhibits a changed solubility in an alkali developing solution under the action of acid and an acid generator that generates acid upon exposure.
For example, a chemically amplified positive resist typically contains a resin component (base resin) that exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component. If the resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then acid is generated from the acid generator within the exposed portions, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resists that use ArF excimer laser lithography and the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 1). Here, the term “(meth)acrylic acid” is a generic term that includes either or both of acrylic acid having a hydrogen atom bonded to the α-position and methacrylic acid having a methyl group bonded to the α-position. The term “(meth)acrylate ester” is a generic term that includes either or both of the acrylate ester having a hydrogen atom bonded to the α-position and the methacrylate ester having a methyl group bonded to the α-position. The term “(meth)acrylate” is a generic term that includes either or both of the acrylate having a hydrogen atom bonded to the α-position and the methacrylate having a methyl group bonded to the α-position.
Further, in order to improve various lithography properties, a resin having a plurality of structural units is currently used as the base resin for a chemically amplified resist. For example, in the case of a positive resist composition, a resin containing a structural unit having an acid dissociable, dissolution inhibiting group that is dissociated by the action of acid generated from the acid generator, as well as a structural unit having a polar group such as a hydroxyl group, a structural unit having a lactone structure or the like is typically used. Among these structural units, a structural unit having a lactone structure is generally considered as being effective in improving the adhesion between the resist film and the substrate, and increasing the compatibility with an alkali developing solution, thereby contributing to improvement in various lithography properties.
In recent years, base resins that include a structural unit which functions as an acid generator have also been used (see, for example, Patent Documents 1 and 2).
Further, sensitizers such as polyphenol compounds have been known for improving the sensitivity to the exposure light sources as those described above (see, for example, Patent Document 3).